During performance assessment of a typical compressor using CFD (“Computational Fluid Dynamics”), it is known to model the solid surfaces boundaries, such as those of blade, vanes, casing and hub, as adiabatic, the computational domain including only the fluid. However, in reality there is some heat transfer that takes place through the solid surfaces mentioned above. If modelled, such heat transfer can result, other numerical errors remaining same, in a different, usually smaller, average fluid temperature than those predicted by a CFD calculation in which the solid boundaries are modelled as adiabatic. A more accurate and non-adiabatic modelling of solid surfaces can therefore result in higher predicted efficiency and realistic stage matching.
A possible state-of-the-art methodology, by means of which the computational domain is extended to the solid region, is known as Conjugate Heat Transfer (CHT) method. Two implementations of such method, for two turbines respectively, are disclosed in “A Conjugate Heat Transfer Method Applied To Turbomachinery” by T. Verstraete, Z. Alsalihi and R. A. Van den Braembussche of the Von Karman Institute for Fluid Dynamics. The approach described in such document is based on a coupling of two codes: a non-adiabatic Navier-Stokes (NS) solver for the flow in the fluid domain and a Finite Element Analysis (FEA) for the heat conduction in the solid parts of the turbines. Continuity of temperature and heat flux at the common boundaries of the NS and FEA models is obtained by an iterative adjustment of the boundary conditions. The non-coinciding grids at the common boundary, requires an interpolation to pass boundary conditions from one model grid to the other and the need for an iterative procedure to obtain the same temperature and heat flux distribution at the boundaries that are common to the NS and FEA calculation domain.
The method described above allows reaching accurate results for the example proposed, but could be significantly improved, particularly when applied to compressors. The method in fact does not take into account: —the casing and hence the transfer of heat between the casing and the surrounding environment; —a stationary fluid domain on the top of the casing to account for heat transfer between the casing and the surrounding environment; —interfaces between models of adjacent elements having different physical properties, for example adjacent elements of the casing, of the rotor and of the stationary fluid domain on the top of the casing, to account of the differences in their circumferential extent due to the differences in blade or vane numbers of the different rotary or stationary stages, respectively, of the compressor.